Strangles is a serious and highly contagious respiratory disease of horses. It is caused by the bacterium Streptococcus equi subspecies equi and is found worldwide.

Clinical Signs

Horses typically develop clinical signs within 3 to 8 days of coming into contact with the bacteria. Not all horses succumb to the disease once exposed. The age, immune status, and number of bacterium all affect whether or not a horse will suffer from the respiratory disease.
For example young horses, with a lower immunity are more likely to suffer from the disease than more mature horses. Signs your horse is suffering from strangles include:

• A nasal discharge, often mucopurulent (green/white and thick)
• Pyrexia (an increased temperature)- anything above 38.6◦C
• Depression; moving around less, the horse may be dull and listless
• Coughing
• Reduced appetite / anorexia
• Swellings under the head and chin as a result of enlarged pus-filled lymph nodes
• The lymph nodes may burst open, draining pus
• The enlarged lymph nodes may occlude the windpipe causing restricted or noisy breathing, thus the name ‘strangles’
• Other body systems may become involved, such as the chest or brain. This is known as ‘Bastard Strangles’ and can present in a variety of ways
• Formation of immune complexes can damage the blood vessels and may result in swelling of the head, neck, limbs and even cause death. This is known as ‘Purpura Haemorhagica’

In classic uncomplicated strangles horses recover uneventfully within a few weeks. Horses shed the bacterium in respiratory secretions and may become carriers for years without any outward signs.

Transmission

Strangles can be spread directly from horse to horse, or indirectly via objects shared between horses, such as grooming tools, rugs, tack and troughs. The risk of transmitting strangles is increased at places with high numbers of horses from different areas such as competitions.

Ways of preventing the spread of the disease include:

• Isolating any new horses for three weeks, monitoring for any clinical signs of strangles and taking their temperatures twice daily.
• Allow a vet to examine all new horses before mixing with other horses on the property.
• Any horses suspected of having strangles should be isolated from other horses immediately. Disinfectant, different equipment and different clothes should be used when dealing with this horse and a vet sought immediately.
• Vaccination using the strangles vaccine should be discussed with your vet. This does not necessarily completely prevent strangles, but will make the episode much shorter and less severe.
• Suspected carriers can be identified using DNA testing on nasopharyngeal washes, performed by your vet.

Figure 2: One of the Strangles Vaccines available in Australia. This one is used by injecting into the muscle. The other vaccine available is administered intranasally.

Treatment

There is no specific treatment for strangles and antibiotics may or may not be indicated. This should be decided by your vet and is considered on a case by case basis. If severe swelling of the abcessated lymph nodes has occurred it may be necessary to lance them to
aid breathing. Nursing care such as warm compresses to encourage bursting of the abscess may be advisable.

The prognosis for most horses following strangles is very good, but some post infection complications can occur such as inflammation of the heart muscle, anaemia, guttural pouch infection, or permanent airway problems. Horses should be isolated for 8 weeks after cessation of clinical signs, and ideally at this time have a swab taken to ensure they are not carriers of the disease.